The present invention concerns a system for regulating the fuel-air mixture in internal combustion engines, a sensor combination for a similar system, and an arrangement for determining the fuel-air mixture in an internal combustion engine.
With the aim of regulating the combustion in an internal combustion engine, so that an optimal stoichiometric combustion takes place for the catalytic converter, sensors in the exhaust system are used, which detect the proportion of residual oxygen in the exhaust gases. Stoichiometric combustion is desirable in order that the catalytic converter shall operate most efficiently and minimise the emission of NOx, HC and CO. The sensors used for this purpose are principally sensitive to the transport of oxygen ions, and are generally called lambda sensors. A characteristic of these sensors is that they are relatively slow to act, and in reality provide an averaged signal that spans several sequential combustion events. A normal step response from such a sensor is that there is a delay in the order of 20 to 30 combustion events before the sensor achieves a new stable output signal level after a change in the actual air-fuel mixture. One disadvantage with this type of sensor is that if it is installed in the exhaust system downstream (with respect to the direction of gas flow) of the exhaust manifold in a multi-cylinder engine, in a position where the exhaust gases from all the cylinders have combined, this can often result in regulation so that individual cylinders run rich while the others run lean, although the combined gas flow indicates stoichiometric combustion has been achieved. The alternative is to arrange a separate sensor in the exhaust gas flow from each individual cylinder, but this would be very expensive. A conventional binary lambda sonde costs at the consumer level about SEK 1200-1400 (xe2x96xa1135-158), and linear lambda sondes cost between 10 and 20 times as much as binary sensors.
By using sensors of the type shown in SE.A.9403218-2(=PCT/SE95/01084) any change in the fuel-air mixture can be detected much more quickly. This sensor is also of a binary type, where the sensor output signal quickly changes from one level to another depending on whether the proportion of hydrogen (H2) in the exhaust gases exceeds or is less than a predetermined value.
The object of the present invention is with only one binary sensor to be able to quickly detect relative deviations from stoichiometric combustion, even for individual combustion events in a multi-cylinder internal combustion engine. From this basis it will easily be possible to regulate all the cylinders equally, so that optimal and similar combustion can take place in all the cylinders. Uneven combustion in a set of cylinders can result in individual cylinders running rich and thereby building up soot deposits. This soot can give rise to so-called hot spots, inducing knocking. In those cylinders which are running lean, the lean combustion itself can increase the risk of knocking. For every type of anti-knock measure the engine deviates from optimal regulation and its fuel consumption increases.
Another reason is to limit emissions, which will be the result if all cylinders can be regulated for stoichiometric combustion. Even small deviations from stoichiometric combustion, for example with excess air content variations in the region of xcex94xcex≈0.001-0.002, will reduce catalytic converter efficiency from 98% to 80-85%.
A further reason is closer regulation of the fuel supply to multi-cylinder internal combustion engines using fuel injectors, permitting lower tolerance claims in the manufacture of the fuel injector components. The need is reduced for a continuous tightening of manufacturing tolerances for fuel injectors, or the alternative of matching individual fuel injectors with similar dynamic responses, with the aim of meeting ever more stringent emission claims.
Yet another purpose is that with a special sensor combination it will be possible to detect relative deviations in both the rich and lean directions away from stoichiometric combustion.
By means of the present invention the fuel supply to each cylinder can be regulated in an optimal manner such that stoichiometric combustion takes place in each cylinder.
By means of the sensor combination of the present invention, relative deviations relative to stoichiometric combustion can be detected, in both rich and lean burn directions, using only a sensor element providing a binary type of output signal.
By means of the general process of the invention detection of the relative deviation from stoichiometric combustion in every cylinder is assured, based upon a sensor of binary type.
Other particularly remarkable characteristics and advantages deriving from the present invention are apparent in the other patent claim characteristic parts and in the subsequent description of an application example. The description of the application example utilises references to the illustrations defined in the following list of drawings.